weird interaction between 2 pedals - can't find the reason

[intripped]

Hello,
I'm having a strange issue using a Catalinbread Belle Epoch in front of a Box Of Rock clone I did.
The two pedals work well by their own, and together with other pedals too.

BUT,
With the BE on, if I turn on the BOR's boost, I get an annoying WREEEEE noise that I can't explain.
the setup is: Guitar - BE - BOR - Amplifier.

- I tried two different BOR clones, built with differently layed-out PCBs, and the result is the same.
- tried different guitars, cables, amplifiers, houses, power supplies (isolated or separated). No joy.

What is really strange is that if I use the BOR's overdrive, there's no noise.
And, as you can see in the attached schematic, the overdrive circuit in its first stage is the exact copy of the boost circuit (aka Super Hard On).
They should behave in the same way. But no, they aren't. WHY!!!???

Schematic: https://files2.soniccdn.com/old/1140704a981b9c69e93.gif

[Andrekp]

Well, first I admit I am not familiar with either circuit.  That said:

I would surmise that the BE is probably very interactive with what's around it.  Sort of like how some fuzzes insist on having a clear shot to your pickups.  have you tried (even if this is not the way you want them arranged in the end) putting some buffered pedals around and between the ones you just built to see if that "breaks the connection" between them?  If that works, then someone here might have some more specific advice to isolate the offender.

(I've had a couple of pedals, one a DIY build, and one a very old fuzz that would show something similar.  They would not make a sound when plugged directly into an amp, but needed a buffer between.  One was a mistake, the other just how it was made.  So things like this can happen.  Again, note fuzzes that need to be first.  Oh, and the "mistake" on the one was an output cap that was leaking big time and raising the signal on significant voltage.) 

Good luck!

[thermionix]

Is the Belle Epoch digital?

[intripped]

Well, first I admit I am not familiar with either circuit.  That said:

I would surmise that the BE is probably very interactive with what's around it.  Sort of like how some fuzzes insist on having a clear shot to your pickups.  have you tried (even if this is not the way you want them arranged in the end) putting some buffered pedals around and between the ones you just built to see if that "breaks the connection" between them?  If that works, then someone here might have some more specific advice to isolate the offender.

I've not tried yet , but for sure I'll use buffers and report the results.

Good luck!

Thanks! I feel like I really need some, here.

Is the Belle Epoch digital?

Yes, the BE is a digital delay, based on the FV1 chip.

I've read around that this pedal has a high output impedance... But if this was the cause, then I should experience the same isssue with the BOR's overdrive (which has the same exact input circuit and impedance of the boost). This is what really puzzles me.

This WREEEEE noise (that is quite loud) is like there's a missing ground reference somewhere.
I've noticed that if I use a wire and create a direct connection between the boxes of the two pedals, it reduces a lot, even if it's still there.
I've already triple checked the ground connections in my BOR, and also opened and disassembled the Belle Epoch and checked the grounds over there as well. Scraped some paint around the holes of potentiometers and footswitch, but this didn't solve the problem.

Next things I'm gonna try:
- breadboard the boost circuit (aka Super Hard On) and see what happens if I use it with the BE;
- try some buffers around;
- call an exorcist.

[antonis]

Next things I'm gonna try:
- breadboard the boost circuit (aka Super Hard On) and see what happens if I use it with the BE;
- try some buffers around;
- call an exorcist.

All good actions...!!!
(if you only reverse the order..) 

[GibsonGM]

Interesting (the wire you tried)...there should already BE a direct connection between them, via the shield/ground of your connecting cable...

[intripped]

Next things I'm gonna try:
- breadboard the boost circuit (aka Super Hard On) and see what happens if I use it with the BE;
- try some buffers around;
- call an exorcist.

All good actions...!!!
(if you only reverse the order..) 

Ouch! 

Interesting (the wire you tried)...there should already BE a direct connection between them, via the shield/ground of your connecting cable...

..and in fact there is: no problems with the cable between pedals. Or with grounds inside the pedals.



I've noticed some other little things:

- if I use a single power supply with daisy chain, the noise reduces a bit;
- using a daisy chained supply, if I touch one or more than one enclosure (including amplifier chassis and power supply enclosure), the noise reduces. The opposite if I use isolated or separated power supplies;
- IMPORTANT: I discovered that if I move the cables around (the jack cables from the guitar and to the amp), I  can find some positions where the noise reduces almost to zero. I move them while touching just the rubber;
- MORE IMPORTANT: if I turn the gain knob of the boost at max, the noise completely disappears!
- the noise is independent from guitar volume or position in the room.

I could for sure be wrong, but it seems to me that there is a strong EMF, and also that this EMF is emanating from the grond net (!). Or a big ground loop that acts like an antenna and picks up environmental noise...

[R.G.]

If you keep adding gain, at some point everything oscillates.

In your first description, you mention that this happens when you turn on the "boost" for the BOR clone. Is that the only time it happens? It looks like the "boost" just inserts another gain stage for yet more gain; this also inverts the low frequency phase of the signal passing through it, yanks more current out of the power supply and inserts more current back into the ground wires locally.

I have not built or tinkered with that variant of the BOR, but on general principles the power supply decoupling looks marginal, given the amount of gain involved. I would have done some distributed RF bypassing; I would also have also cut the bandwidth of each section down to audio, not letting it go into RF.

But you're saying that the BOR clone does not do this by itself, only when the delay is in front of it, and only when boost is turned on. Leaving aside the question of why you'd want to put a delay in front of a distortion pedal, the question is then how are the pedals interacting?

Ground seems like a likely place to start. If isolated-ground power makes it worse, that seems to imply that ground is in the mix somewhere, even if each pedal is OK by itself, and OK in all instances except delay into distortion in boost mode and high gain. This is further compounded by the observation that running a separate wire for ground changes things, and that touching the signal ground changes things.

Without the pedals and setup to look at, I can only speculate. The external ground wire changing anything is a huge red flag. The two units should be sufficiently grounded by the signal cable. Add in isolated-ground power supplies making it worse and you have a strong indicator that something is not well and properly grounded in one or the other pedal. Actually, I'd start looking inside the BE, as the BOR will make any grounding issues there worse by the number of DB of gain it adds.

One other issue that may come up. I would expect it to be above audio in most cases, but the BE cannot remove all ultrasonic and RF components from its output signal. This usually doesn't matter, but with enough gain in the BOR, this can be resurrected from the noise and wind up biting you. Accordingly, if I were faced with this problem, I'd start looking at grounding, power bypassing and signal bandwidth limitations in the BE in some detail.

[Andrekp]

Not that he needs MY agreement, but I agree with RG.  Based on your latest, start looking at ground.

But I would also not dismiss the cables, until you KNOW you can.  I once had a pedal problem that I just could find.  Tried everything.  Was using a cable that worked fine.  Caused no problems at all until I put the one pedal in.  BY ACCIDENT I changed cables and the problem went away.  Turns out there was some tiny problem in that cable that otherwise remained hidden.  Very odd.   Not saying it's an issue here, but you just never know.  Don't rules anything out until you KNOW you can.

[idy]

Yeah, are you sure you need to put a delay pedal before an overdrive? Not that we discourage crazy around here or anything...

[GibsonGM]

Interesting (the wire you tried)...there should already BE a direct connection between them, via the shield/ground of your connecting cable...

Have you actually tested their continuity, their resistance?

[induction]

Yeah, are you sure you need to put a delay pedal before an overdrive? Not that we discourage crazy around here or anything...

I see no craziness in this. I do it all the time.

[intripped]

If you keep adding gain, at some point everything oscillates.

In your first description, you mention that this happens when you turn on the "boost" for the BOR clone. Is that the only time it happens? It looks like the "boost" just inserts another gain stage for yet more gain; this also inverts the low frequency phase of the signal passing through it, yanks more current out of the power supply and inserts more current back into the ground wires locally. 

the BOR is a 2-effects-in-a box pedal: there are two independent circuits, an overdrive and a boost (the boost is placed after the overdive).

this is the situation:
BE + overdrive = ok
BE + boost = WREEEEEE
BE + overdrive + boost = ok
(boost alone = ok)

so it's not a "yet more gain" scenario (that brings up the background noise).

I have not built or tinkered with that variant of the BOR, but on general principles the power supply decoupling looks marginal, given the amount of gain involved. I would have done some distributed RF bypassing; I would also have also cut the bandwidth of each section down to audio, not letting it go into RF.

with RF bypassing you mean some small capacitors (pF range) between the audio path and ground? i could try and add one at the input of the boost

also about power decoupling (hope i correctly understand what power decoupling is): i've duplicated the power filtering in the BOR, so now each circuit has its own power section. still no joy.

[...]the question is then how are the pedals interacting?

here probably i've not chosen the best english word... i didn't know another way for briefly describing the issue i'm experiencing.
or maybe you're asking me if the pedals works normally despite the noise? the answer is yes, the delay delays and the boost boosts, there's only this loud noise on the top.

Ground seems like a likely place to start. If isolated-ground power makes it worse, that seems to imply that ground is in the mix somewhere, even if each pedal is OK by itself, and OK in all instances except delay into distortion in boost mode and high gain. This is further compounded by the observation that running a separate wire for ground changes things, and that touching the signal ground changes things.

Without the pedals and setup to look at, I can only speculate. The external ground wire changing anything is a huge red flag. The two units should be sufficiently grounded by the signal cable. Add in isolated-ground power supplies making it worse and you have a strong indicator that something is not well and properly grounded in one or the other pedal. Actually, I'd start looking inside the BE, as the BOR will make any grounding issues there worse by the number of DB of gain it adds.

yes, it does look like a ground issue, but i really can't find the solution.
i've already looked inside the BE pedal, and checked for grounds on the jacks, PCB and enclosure.
if it was a missing ground connection of one or more components in the PCB, well, it would be quite a task to find it out. maybe later i'll try and see what i can do... the BE is also quite crammed inside, with SMD and stuff.

One other issue that may come up. I would expect it to be above audio in most cases, but the BE cannot remove all ultrasonic and RF components from its output signal. This usually doesn't matter, but with enough gain in the BOR, this can be resurrected from the noise and wind up biting you. Accordingly, if I were faced with this problem, I'd start looking at grounding, power bypassing and signal bandwidth limitations in the BE in some detail.

it doesn't seem to be an amplified backround noise, also because it's not happening with overdrive + boost, but just with the boost alone.
as i said before, i'll try and have another look inside the BE and see what i can do, even if i'm afraid that this goes a little over my capabilities.

Not that he needs MY agreement, but I agree with RG.  Based on your latest, start looking at ground.

But I would also not dismiss the cables, until you KNOW you can.  I once had a pedal problem that I just could find.  Tried everything.  Was using a cable that worked fine.  Caused no problems at all until I put the one pedal in.  BY ACCIDENT I changed cables and the problem went away.  Turns out there was some tiny problem in that cable that otherwise remained hidden.  Very odd.   Not saying it's an issue here, but you just never know.  Don't rules anything out until you KNOW you can.

i've already tried different guitars, amplifiers, cables, houses, power supplies, even two different BOR clones.

Interesting (the wire you tried)...there should already BE a direct connection between them, via the shield/ground of your connecting cable...

Have you actually tested their continuity, their resistance?

yes, i did.
this strange behaviour perhaps is related to the fact that i was touching the wire, so my body mass was in the game...

-----------------------------------

the most important thing that i discovered in my tests, is that if i turn the Boost pot at max, the noise completely disappears!
and i don't mean "it reduces to almost zero", it does actually disappear: while i turn the pot i hear the noise going up in level, until it becomes very loud, and after a sort of "thump" or strong motorboating, silence is back. Everything works, volume level is very high (as it should be with the gain pot at max) but there's no more noise.

you probably know about the "crackle ok" pots in the BOR and other Zvex pedals.
coul this be related to the problem?

Yeah, are you sure you need to put a delay pedal before an overdrive? Not that we discourage crazy around here or anything...

I see no craziness in this. I do it all the time.

yeah! 

thanks to all!

[PRR]

> if i turn the Boost pot at max, the noise completely disappears!  and i don't mean "it reduces to almost zero", it does actually disappear: while i turn the pot i hear the noise going up in level, until it becomes very loud, and after a sort of "thump" or strong motorboating, silence is back.

Confirming R.G.'s remark: enough gain, everything oscillates.....

BUT in this case turning the signal pot wiper to the top is *reducing* gain around the oscillation loop.

This is A Clue.

It strongly suggests the sneak-around signal come in at the boost pot *wiper*. When mid-turn, the wiper is a high impedance, and susceptible to sneak leaks. When full-up it probably connects to some *low* impedance source, which sucks-up the leakage. And yes, typically when loop-gain is 1.00001 it squeals, when loop gain is 0.9999 the squeal quits, so the squeal-stop may be very sharply defined.

Where does that Boost pot wiper wire go? Specifically what does it "go past" which might be a high-level version of what is coming from Boost pot wiper?   

[intripped]

Here is the schematic of the BOR pedal, you can see the overdrive and the boost circuits.
If it's a gain related issue, why it doesn't happen when I use the overdrive? Or the overdrive and the boost?
It only happens with the boost alone.

[R.G.]

the BOR is a 2-effects-in-a box pedal: there are two independent circuits, an overdrive and a boost (the boost is placed after the overdive).
[...]
BE + boost = WREEEEEE
[...]
so it's not a "yet more gain" scenario (that brings up the background noise).

OK.

with RF bypassing you mean some small capacitors (pF range) between the audio path and ground? i could try and add one at the input of the boost

also about power decoupling (hope i correctly understand what power decoupling is): i've duplicated the power filtering in the BOR, so now each circuit has its own power section. still no joy.

For RF bypassing on the power supply, connect 0.01 uF to 0.1uF CERAMIC capacitors from + to ground as close to the circuit being powered as possible.

For removing hidden RF from the signal lines, insert 47pF to 100pF CERAMIC capacitors from the signal line to ground, ideally also inserting 10R to 100R series resistors before the caps. This adds some resistance to turn the RF energy to heat and the capacitance shunts remaining RF to grround. It's a central tenet of low noise design to limit your amplifier's bandwidth to only the expected signals, not dramatically more or less.

maybe you're asking me if the pedals works normally despite the noise? the answer is yes, the delay delays and the boost boosts, there's only this loud noise on the top.

Hmmm. It is common that self oscillation is so intense that no actual signal can get through. If the signal is getting through AND the whine is running, it's not a simple self oscillation, most likely.

This makes me think that maybe the overdrive is oscillating when only the BE and boost are being used, and that oscillation is being coupled into the BE plus boost signal path.

Some overdrives oscillate when their inputs are left open by bypass switching. Does your bypass arrangement ground the input to the overdrive when only the boost is being used?

the most important thing that i discovered in my tests, is that if i turn the Boost pot at max, the noise completely disappears!
and i don't mean "it reduces to almost zero", it does actually disappear: while i turn the pot i hear the noise going up in level, until it becomes very loud, and after a sort of "thump" or strong motorboating, silence is back. Everything works, volume level is very high (as it should be with the gain pot at max) but there's no more noise.

you probably know about the "crackle ok" pots in the BOR and other Zvex pedals.
coul this be related to the problem?

Yeah, I always chuckle at the idea of "crackle OK". The "crackle OK" pots actually change the DC conditions in the stage with the pot. Imperfections in the pot open and close the wiper contact momentarily, and this causes the MOSFET to suddenly change bias points; that's what's heard as crackle. But in any case, it does change both the AC gain and the DC bias point of the boost circuit as you turn it.

That makes me think that it may also be significant that the whine begins as you turn the boost control up, but then it quits. If I had this on my workbench, I would put a voltmeter on the drain of the boost pot and look for how the voltage changes as I turn the boost pot. I don't yet know what to do with that information, but it might suggest something.

@PRR; I'd agree with you on the impedance maximizing for a pot at mid travel, excepting that in this case the pot is hooked up as a variable source resistance to ground, so it doesn't maximize in the middle like a  volume control would. It could still be giving issues with signal injection if it runs near a strong signal point on its path, but it's a low impedance and that makes signal injection in the audio band more unlikely. Not impossible, but much less likely.

Let's do some recap. Looking for interactions amounts to thinking of all the ways things could interact, then eliminating them one by one with tests until one or more conditions are found that reliably cause changes in the observed result.

So: is it the environment? Is the interaction affected by different cables? guitars? amplifiers? houses (i.e. EMI field conditions and electrical power supply)?  We're told those were elimiinated.

Next up for possible conditions are problems with soldering and wiring, the predictable bane of all DIY pedals. We're told that's not the issue, as the pedals work fine in all conditions by themselves, and that even substituting in another same-circuit-but-different-manufacture for the boost+OD causes the same result.

Next up I'd consider power supply and grounding as a cause of oscillation issues. We are told that the grounds have been well and truly examined, and that they are continuous. There is that little oddity about running a ground wire causing a change in the whining. That's very odd if the grounds are actually OK.

We're told that the whining occurs if the two pedal lumps (i.e. the BE and the OD+boost) are supplied from isolated power supplies, but is reduced if the power supplies are daisy chained. Again, very odd.

I would at this point run the OD+boost from a battery and see if it still whines.

I had suggested going off to chase RF ghosts by using ceramic bypasses and RF signal blocking. There still might be something there.

I think that the fact that the BE plus the boost with the OD bypassed still passing signal during the whine points to the OD circuit being the source of the whining.

I would look at the whining signal on an oscilloscope and note whether the frequency or size of the oscillation changed when turning the boost control. I would also test carefully whether tuning the controls on the >OD< changes the whining while the BE and boost are connected and whining.

[R.G.]

I forgot to mention - it is always possible that you have offended some minor deity in some way.

[intripped]

Please standby, (and also please forgive me for not having noticed it before):

The problem seems to be related to the Boost circuit only.

I didn't notice it before, because the noise without the BE is very subtle. but there is.

with this setup:
Guitar, BOR, amplifier
The pick up selector and the volume pot on the guitar become scratchy (!), and if I turn back a little the volume pot, the noise becomes more evident. With the volume pot almost at zero the noise disappears (!?).
There's a slight difference when I touch the strings, but just slight.

So the Boost circuit seems to send back something on the signal path.

There's no DC voltage at the input of the pedal; I've measured it in the mV range, nothing.

Maybe some kind of interference coming from the power supply.
I'm gonna do a test with a battery and report back.

Again, please forgive me for not having noticed it before.
There's still a mistery, though, because even if the BE is out of the game, I still can't understand what's going on, and why the overdrive is silent and without issues.

[intripped]

RG and PRR, thanks for your detailed answers! (Forgot to say it before)

I will do other tests, following all your hints.

Some other clues and notes:

- actually the noise is not a whine, is more similar to the noise you get when you insert a jack into the amp and touch with your hand the other end of the cable. Only not so loud, and probably higher in pitch.
- my bypass arrangement does ground the input of the circuits, BUT, in bypass I can hear the scratching of the gain pot of the overdrive (in background). I'm not sure about the gain pot of the Boost, it's late in the night here now and I can't do more tests at the moment.
Also, I'll not be at home for the next week, so everything has to be procrastinated.

Thanks again and see you next week!

[PRR]

> I always chuckle at the idea of "crackle OK".

I had crystal-controlled transmitters. In one, the crystal can had a sticker "rattle OK". Indeed it rattled and worked fine. Bit of solder come loose after the can was sealed, but not in a bad place? The transmitters were "cost effective", not high-class, so I suppose they would accept functional rejects.

> ...impedance maximizing for a pot at mid travel, excepting that in this case....

I guess I missed that. Sorry for the side-path.